With Vsynch enabled, and a decent amount of video memory, triple buffering will be faster. You know how double buffering works, right? At any time, one buffer is being drawn to and the other being displayed. The problem is, with vsynch on, you can't display the buffer it just finished drawing until the next vertical retrace on the monitor, which means that you'll sit there idle for a little bit. Triple buffering gives the computer another frame to draw while waiting for the vsynch.
If Vsynch is disabled, then it doesn't matter, and you might as well save your vid mem for textures.